Thermodynamic Signatures of Structural Transitions and Dissociation of Charged Colloidal Clusters: A Parallel Tempering Monte Carlo Study.

Computational simulation of colloidal systems make use of empirical interaction potentials that are founded in well-established theory. In this work, we have performed parallel tempering Monte Carlo (PTMC) simulations to calculate heat capacity and to assess structural transitions, which may occur in charged colloidal clusters whose effective interactions are described by a sum of pair potentials with attractive short-range and repulsive long-range components. Previous studies on these systems have shown that the global minimum structure varies from spherical-type shapes for small-size clusters to Bernal spiral and "beaded-necklace" shapes at intermediate and larger sizes, respectively. In order to study both structural transitions and dissociation, we have organized the structures appearing in the PTMC calculations by three sets according to their energy: (i) low-energy structures, including the global minimum; (ii) intermediate-energy "beaded-necklace" motifs; (iii) high-energy linear and branched structures that characterize the dissociative clusters. We observe that, depending on the cluster, either peaks or shoulders on the heat-capacity curve constitute thermodynamics signatures of dissociation and structural transitions. The dissociation occurs at T=0.20 for all studied clusters and it is characterized by the appearance of a significant number of linear structures, while the structural transitions corresponding to unrolling the Bernal spiral are quite dependent on the size of the colloidal system.

Microsolvation of Li+ in a Mixture of Argon and Krypton: Unveiling the Most Stable Structures of the Clusters.

The microsolvation of Li+ by both argon and krypton atoms has been studied based on a new potential energy surface that includes two- and three-body interactions; the potential terms involving the lithium ion were calibrated with CCSD(T)/aug-cc-pVQZ energies after being corrected for the basis-set superposition error. The structures of the Li+Ar nKr m ([Formula: see text]) clusters arising from global optimization show a first solvation shell preferentially occupied by krypton atoms. These binary-solvent microsolvation clusters are most stable when the total number of krypton (argon) atoms occupy the first (second) solvation shell.

Correction: Solvation of Li+ by argon: how important are three-body forces?

Correction for 'Solvation of Li+ by argon: how important are three-body forces?' by Frederico V. Prudente et al., Phys. Chem. Chem. Phys., 2017, 19, 25707-25716.

Solvation of Li+ by argon: how important are three-body forces?

A new analytical potential for Li+Ar2 including three-body interactions has been modeled by employing ab initio energies that were calculated within the CCSD(T) framework and a quadruple-zeta basis-set (i.e., cc-pVQZ for lithium and aug-cc-pVQZ for argon) and, then, corrected for the basis-set superposition error (BSSE) with the counterpoise method. Departing from this function, we have constructed the potential energy surface for Li+Arn clusters by summing over all two-body and three-body terms. We have employed our evolutionary algorithm (EA) to perform a global geometry optimization that allows for the study of a Li+ ion microsolvated with argon atoms. For the smaller clusters, the putative global minimum geometry obtained for the analytical potential has been used as a starting point for an ab initio optimization at the MP2 level. For clusters up to n = 10, the energetics and structures from the analytical potential energy surface (PES) that includes three-body interactions show good agreement with the corresponding ones optimized at the ab initio level. Removing the three-body terms from the analytical PES leads to global minima that fail to represent the main energetic features and the structures become wrong in the case of the Li+Ar2, Li+Ar3 and Li+Ar10 clusters. For n > 10, the comparison between potentials with and without three-body forces shows significant structural and energetic differences for most of the cluster sizes.